The present invention relates to a rotor for an electric motor, and more particularly to a rotor of this kind which is designed to be suitable for fixing in place a cylindrical permanent magnet.
Japanese Utility Model Laid-Open No. 97588/1984 discloses a conventional rotor for an electric motor. A description of such a conventional rotor for an electric motor will be given with reference to FIG. 4 showing a longitudinal sectional view of an electrically-operated compressor of the sealed-type.
In the drawing, reference number 24 designates a sealed housing within which a compression mechanism 22 and an electric motor 23 are accommodated.
The electric motor 23 will be described in detail. Reference number 25 designates a stator. This stator 25 is secured to the internal wall of the sealed housing 24. Reference number 26 designates a permanent magnet rotor. The permanent magnet rotor 26 comprises an iron core (yoke) 28, a permanent magnet 29, a surface reinforcing member 34, and an aluminum diecast member 31. The permanent magnet 29 is provided on the outer periphery of the iron core 28.
That is, the surface reinforcing member 34 is provided for the purpose of securing the permanent magnet 29 to the outer peripheral surface of the iron core 28. The aluminum diecast member 31 is provided for the purpose of connecting the iron core 28 and the permanent magnet 29.
However, a conventional rotor having such a structure encounters problems with respect to both productivity and performance. These problems include the following:
(i) The yoke and the permanent magnet have to be assembled by use of adhesive before they are placed into a diecast mold;
(ii) Since it is necessary to prevent penetration of diecast material between the surface reinforcing member and the wall of the diecast mold, the surface reinforcing member cannot be made very thin; and
(iii) The thermal affect of diecasting makes it impossible to obtain a high degree of precision.